Steve Bertrand wrote:
> > Steve Bertrand wrote:
> > > I got it...
> > >
> > > for my $item (@clean) {
> > > if (! grep ($_ eq $item, @array)) {
> > > push (@array, $item);
> > > print "$item\n";
> > > }
> > > }
> >
> > FWIW, this is a FAQ (see "perldoc -q duplicate"). If the array
> > elements can be compared with string semantics (as you are doing
> > here), the following will work:
> >
> > my @array = do { my %seen; grep !$seen{$_}++, @clean };
>
> Thank you for the info...but pardon my ignorance. I'd just like to
> understand what is happening there. Is grep adding to the array the
> keys in the hash that have values that have not been incremented?
Erm, sort of...
grep() is a function that returns a list. Since it's the last expression
evaluated in the do { } block, that list becomes the result assigned to
@array.
grep() takes an input list (the elements of @clean) and returns a list
composed of each element from @clean for which the following expression is
true:
!$seen{$_}++
Within the expression $_ represents the current element of @clean being
examined. What's happening is that the hash entry $seen{$_} is being
incremented by one. The value of the expression is the hash entry $seen{$_}
BEFORE incrementing.
So, for any given string coming from @clean, the hash entry $seen{$_} will
be undef the first time, and then 1 the second time, 2 the third time, and
so on. The ! operator logically negates the value, so the entire expression
returns the following pattern for a repeated series of the same value:
true, false, false, false, ...
In other words, the expression is true only for the first occurence of each
different entry in @clean. Since grep() only passes through the elements for
which the expression is "true", only the first occurence of each different
entry in @clean makes it into @array, thus "removing" the duplicates, QED.
The do { } block is there because we need a temporary hash. The hash goes
away at the end of the do { } block since we don't need it after grep() is
finished.
n.b. there's another way you can do this:
@array = do { my %h; @[EMAIL PROTECTED] = (); keys %h };
or similarly,
@array = keys %{{map +($_, 1), @clean}};
These do not preserve the order of the values in @clean however.
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